This invention relates to an intrusion detector, and more particularly to a motion detection system utilizing a simple wide field of view optical system with a thermopile detector which is so constructed as to produce opposite polarity output signals as an object in the field of view of the optical system moves across the thermopile to produce a sequence of motion which with proper processing and logic circuitry indicates the presence of an intruder.
Many intrusion detector systems have been proposed, both active and passive in nature. The active systems generally require a source of radiant energy in the form of light or other radiation which is projected into or covers a predetermined area which, when crossed by the intruder, interrupts or alters the radiation to cause an alarm. Since all active systems require a source of radiation or a transmitter, additional equipment is needed and is a source of failure as well as being more easily detected by the intruder. The passive type system utilizes the radiation in the form of infrared which is generated by the intruder and picked up by a suitable infrared detector and processed to give an alarm. Noise spikes and other forms of interference in many of these systems generate unwanted alarms. Various passive systems have been suggested which provide a plurality of detector elements viewing separate or overlapping fields of view in an attempt to overcome these problems. The present invention is a passive system which has a simple optical system covering a wide field of view which utilizes a single thermopile detector device directed to the solution of these problems.